(→‎Black screen on lid up with light-locker: Removed section, as original writer was not able to reproduce this error on same machine, making this section's validity effectively null and void until it is reproductable.)

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[[Category:Display managers]]

[[Category:Display managers]]

[[es:LightDM]]

[[es:LightDM]]

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{{Article summary start}}

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[[fr:LightDM]]

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{{Article summary text|Provides an overview and setup of the Light Display Manager.}}

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[[ja:LightDM]]

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{{Article summary heading|Related}}

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[[ru:LightDM]]

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{{Article summary wiki|Display Manager}}

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[[zh-hans:LightDM]]

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{{Article summary end}}

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{{Related articles start}}

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{{Related|Display manager}}

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{{Related|GDM}}

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{{Related|LXDM}}

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{{Related articles end}}

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[http://www.freedesktop.org/wiki/Software/LightDM Lightdm] LightDM is a cross-desktop display manager that aims to be the standard display manager for the X.org X server.

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[http://www.freedesktop.org/wiki/Software/LightDM LightDM] is a cross-desktop [[display manager]]. Its key features are:

More details about LightDM's design can be found [http://www.freedesktop.org/wiki/Software/LightDM/Design here].

== Installation ==

== Installation ==

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Currently, {{AUR|lightdm}} resides in the [[AUR]]. Install it like any other AUR package.

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[[Install]] {{Pkg|lightdm}}. Note that stable releases are even-numbered (1.8, 1.10) while development releases are odd-numbered (1.9, 1.11). These development releases are available with {{AUR|lightdm-devel}}. Also available is {{AUR|lightdm-bzr}}.

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=== Greeter===

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You will probably want to install a greeter. A greeter is a GUI that prompts the user for credentials, lets the user select a session, and so on. It's possible to use LightDM without a greeter, but only if an automatic login is configured. The reference greeter is {{Pkg|lightdm-gtk-greeter}}. LightDM attempts to use this greeter when started unless configured to do otherwise.

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The official repositories contain the following alternative greeters.

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* {{Pkg|lightdm-kde-greeter}}: A greeter used with KDE4.

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* lightdm-deepin-greeter ({{Pkg|deepin-session-ui}}): A greeter from the [[Deepin]] project.

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Other alternative greeters are available in the [[AUR]].

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* {{AUR|lightdm-webkit2-greeter}}: A greeter that uses Webkit2 for theming. It supersedes {{AUR|lightdm-webkit-greeter}}.

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* {{AUR|lightdm-unity-greeter}}: The greeter used by Ubuntu's [[Unity]].

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* {{AUR|lightdm-pantheon-greeter}}: A greeter from the elementary OS project.

You can set the default greeter by changing the {{ic|[Seat:*]}} section of the LightDM configuration file, like so:

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{{hc|/etc/lightdm/lightdm.conf|2=

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[Seat:*]

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...

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greeter-session=lightdm-yourgreeter-greeter

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}}

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Which greeters are available? What values may be assigned to the {{ic|greeter-session}} option? Each {{ic|.desktop}} file in the {{ic|/usr/share/xgreeters}} directory denotes an available greeter. In this example, the {{ic|lightdm-gtk-greeter}} and {{ic|lightdm-kde-greeter}} greeters are available:

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$ ls -1 /usr/share/xgreeters/

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lightdm-gtk-greeter.desktop

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lightdm-kde-greeter.desktop

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== Enabling LightDM ==

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Make sure to [[enable]] {{ic|lightdm.service}} so LightDM will be started at boot, see also [[Display manager#Loading the display manager]].

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== Command line tool ==

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LightDM offers a command line tool, {{ic|dm-tool}}, which can be used to lock the current seat, switch sessions, etc, which is useful with 'minimalist' window managers and for testing. To see a list of available commands, execute:

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$ dm-tool --help

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=== User switching ===

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{{Accuracy|Is this warning inappropriate? Don't {{ic|dm-tool lock}} and {{ic|dm-tool switch-to-greeter}} do the equivalent of calling {{ic|loginctl lock-session}}? If your screen locker doesn't register with ''logind'' then there's nothing {{ic|dm-tool ...}} can do - but that's not LightDM's fault. This issue is well known and touched upon [[List_of_applications#Screen_lockers|here]] and [[XScreenSaver#Lock_on_suspend|here]].}}

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{{Warning|1=The use of lightDM's built-in screen lockers like {{ic|dm-tool lock}} or {{ic|dm-tool switch-to-greeter}} [https://bbs.archlinux.org/viewtopic.php?pid=1712213#p1712213 are '''not''' recommended]. Use [[#Lock the screen using light-locker|light-locker]] or something from [[List of applications/Security#Screen lockers]].}}

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LightDM's ''dm-tool'' command can be used to allow multiple users to be logged in on separate ttys. The following will send a signal requesting that the current session be locked and then will initiate a switch to LightDM's greeter, allowing a new user to log in to the system.

To change the default greeter ({{AUR|lightdm-gtk-greeter}}) edit the lightdm PKGBUILD and change the line

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You can set the background to a hex color or an image. Some greeters offer more robust background options like background selection from the login screen, random backgrounds, etc.

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--with-greeter-session=lightdm-gtk-greeter

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to

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--with-greeter-session=lightdm-yourgreeter-greeter

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To change default greeter by modifying lightdm.conf. <br>

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==== GTK+ greeter ====

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{{bc|greeter-session&#61;lightdm-kde-greeter}}Lightdm.conf can be found at :<br>

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{{bc|/etc/lightdm/lightdm.conf}} <br>

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== Enabling Lightdm ==

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You can use the {{Pkg|lightdm-gtk-greeter-settings}} gui.

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=== Using Initscripts ===

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Lightdm can be loaded on startup by entering it in the daemons array in {{ic|rc.conf}}, or by modifying {{ic|inittab}} so it points to lightdm:

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x:5:respawn:/usr/sbin/lightdm >& /dev/null

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{{Note|The 'inittab' method is the preferred method to use a graphical greeter. See [[Display_Manager#inittab_method]].}}

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{{Note|Lightdm needs [[dbus]] to be running. If you get an error about "respawing too fast" you may have forgotten this. Ensure that dbus is in your [[DAEMONS]] array in {{ic|rc.conf}}.}}

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Users wishing to customize the wallpaper on the greeter screen need to edit {{ic|/etc/lightdm/lightdm-gtk-greeter.conf}} and define the {{ic|background}} variable under the {{ic|[greeter]}} section. For example:

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=== Using Systemd ===

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{{hc|/etc/lightdm/lightdm-gtk-greeter.conf|2=

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For systems using systemd, Lightdm also has a systemd service file, start it with {{ic|systemctl start lightdm.service}} or enable it for boot with {{ic|systemctl enable lightdm.service}}.

{{Note|It is recommended to place the PNG or JPG file in {{ic|/usr/share/pixmaps}} since the LightDM user needs read access to the wallpaper file.}}

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=== Testing ===

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===== GTK3 Dark Theme =====

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Install xorg-server-xephyr:

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GTK3 introduced "dark" alternate color palettes for themes, but lightdm-gtk-greeter does not yet support specifing one natively. A workaround is to override the theme with an evironment variable in {{ic|/usr/share/xgreeters/lightdm-gtk-greeter.desktop}} For example:

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pacman -S xorg-server-xephyr

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{{hc|/usr/share/xgreeters/lightdm-gtk-greeter.desktop|2=

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Run lightdm as a X application:

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[Desktop Entry]

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lightdm --test-mode --debug

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Name=LightDM GTK+ Greeter

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Comment=This runs the GTK+ greeter, it should only be run from LightDM

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Exec=env GTK_THEME=Adwaita:dark lightdm-gtk-greeter

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Type=Application

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X-Ubuntu-Gettext-Domain=lightdm

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}}

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== Optional Configuration and Tweaks ==

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==== Webkit2 greeter ====

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=== Changing Background Images/Colors ===

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Users wishing to customize the wallpaper on the greeter screen need to edit {{ic|/etc/lightdm/lightdm-gtk-greeter.conf}} defining the '''background''' variable.

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Example:

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The {{AUR|lightdm-webkit2-greeter}} allows you to choose a background image directly on the login screen. It also offers an option to display a random image each time it starts. By default, images are sourced from {{ic|/usr/share/backgrounds}}. You can change the background images directory by editing {{ic|lightdm-webkit2-greeter.conf}}. For example:

Alternatively, you can edit the {{ic|Background}} variable in {{ic|lightdm-kde-greeter.conf}} :

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{{hc|/etc/lightdm/lightdm-kde-greeter.conf|2=

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[greeter]

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theme-name=classic

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[greeter-settings]

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Background=/usr/share/archlinux/wallpaper/archlinux-underground.jpg

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BackgroundKeepAspectRatio=true

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GreetMessage=Welcome to %hostname%

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}}

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=== Changing your avatar ===

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{{Tip|If you are using KDE, you can change your avatar in KDE System Settings.}}

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First, make sure the {{pkg|accountsservice}} package from the [[official repositories]] is installed, then set it up as follows, replacing {{ic|''username''}} with the desired user's login name. The ''.png'' file extension should not be included in the filename.

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* Edit or create the file {{ic|/var/lib/AccountsService/users/''username''}}, and add the lines

{{Note|Make sure that both created files have 644 permissions, use [[chmod]] to correct them.}}

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=== Sources of Arch-centric 64x64 icons ===

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The {{AUR|archlinux-artwork}} package from the [[AUR]] contains some nice examples that install to {{ic|/usr/share/archlinux/icons}} and that can be copied to {{ic|/usr/share/icons/hicolor/64x64/devices}} as follows:

Edit the LightDM configuration file and ensure these lines are uncommented and correctly configured:

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{{hc|/etc/lightdm/lightdm.conf|2=

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[Seat:*]

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autologin-user=''username''

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}}

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You must be part of the {{ic|autologin}} group to be able to login automatically without entering your password:

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# groupadd -r autologin

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# gpasswd -a ''username'' autologin

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LightDM logs in using the session specified in the {{ic|~/.dmrc}} of the user getting logged in automatically. To override this file, specify {{ic|autologin-session}} in {{ic|lightdm.conf}}:

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{{hc|/etc/lightdm/lightdm.conf|2=

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[Seat:*]

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autologin-user=''username''

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autologin-session=''session''

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}}

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{{Note|GNOME users, and by extension any gnome-keyring user will have to set up a blank password to their keyring for it to be unlocked automatically.}}

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=== Enabling interactive passwordless login ===

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LightDM goes through PAM so you must configure the lightdm configuration of PAM:

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{{hc|/etc/pam.d/lightdm|2=

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#%PAM-1.0

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'''auth sufficient pam_succeed_if.so user ingroup nopasswdlogin'''

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auth include system-login

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...

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}}

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You must then also be part of the {{ic|nopasswdlogin}} group to be able to login interactively without entering your password:

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# groupadd -r nopasswdlogin

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# gpasswd -a ''username'' nopasswdlogin

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{{Note|GNOME users, and by extension any gnome-keyring user may have to follow the instructions at the end of the previous section on enabling autologin.}}

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To create a new user account that logs in automatically and additionally able to login again without a password the user can be created with supplementary membership of both groups, e.g.:

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# useradd -mG autologin,nopasswdlogin -s /bin/bash ''username''

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=== Hiding system and services users ===

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To prevent system users from showing-up in the login, install the optional dependency {{Pkg|accountsservice}}, or add the user names to {{ic|/etc/lightdm/users.conf}} under {{ic|hidden-users}}. The first option has the advantage of not needing to update the list when more users are added or removed.

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=== Migrating from SLiM ===

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{{Merge|Display Manager|Not LightDM specific (or even SLiM specific for that matter as [[XDM]] also uses [[xinitrc]]). Perhaps this merits a one-liner somewhere on the [[Display Manager]] page?}}

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Move the contents of [[xinitrc]] to [[xprofile]], removing the call to start the [[window manager]] or [[desktop environment]].

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=== Login using ~/.xinitrc ===

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See [[Display manager#Run ~/.xinitrc as a session]].

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=== NumLock on by default ===

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Install the {{Pkg|numlockx}} package and then edit {{ic|/etc/lightdm/lightdm.conf}}:

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{{hc|/etc/lightdm/lightdm.conf|2=

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[Seat:*]

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greeter-setup-script=/usr/bin/numlockx on

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}}

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=== Default session ===

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Lightdm, like other DMs, stores the last-selected xsession in {{ic|~/.dmrc}}. See [[Display manager#Session configuration]] for more info.

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=== Adjusting the login window's position ===

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{{Note|It is recommended to place png or jpg files in /usr/share/pixmaps since the lightdm user needs read access to the wallpaper file.}}

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==== GTK+ greeter ====

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Users wishing to have a flat color (no image) may simply set the '''background''' variable to a hex color.

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Users need to edit {{ic|/etc/lightdm/lightdm-gtk-greeter.conf}} and enter a value for the {{ic|position}} variable. It accepts {{ic|x}} and {{ic|y}} values, either absolute (in pixels) or relative (in percent). Each value can also have an additional anchor location for the window, {{ic|start}}, {{ic|center}} and {{ic|end}} separated from the value by a comma.

Example:

Example:

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background=#000000

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=== Changing the Icon ===

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position=200,start 50%,center

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Users wishing to customize the icon on the greeter screen need to edit {{ic|/etc/lightdm/lightdm-gtk-greeter.conf}} defining the '''logo''' variable.

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=== VNC Server ===

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Lightdm can also be used to connect to via VNC. Make sure to install {{pkg|tigervnc}} on the server side and optionally as your VNC client on the client PC.

Edit the LightDM configuration file as shown below. Note that {{ic|listen-address}} configures the VNC to only listen to connections from localhost. This is used to only allow connections via [[TigerVNC#On_the_client|SSH and port forwarding]]. On the SSH client, make sure that you use {{ic|localhost:5900}} for the tunnel destination; using {{ic|127.0.0.1:5900}} or {{ic|::1:5900}} is not reliable on dual stack network connections. If you want to allow insecure connections you can disable this setting.

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{{hc|/etc/lightdm/lightdm.conf|2=

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[VNCServer]

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enabled=true

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command=Xvnc -rfbauth /etc/vncpasswd

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port=5900

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listen-address=localhost

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width=1024

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height=768

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depth=24

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}}

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Now open an SSH tunnel and connect to localhost as described in [[TigerVNC#On the client]].

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{{Note|If you get a blank screen upon opening the VNC connection, try a different LightDM greeter.}}

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=== Lock the screen using light-locker ===

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{{Pkg|light-locker}} is a simple screen locker using LightDM to authenticate the user. Once it is installed and running you can lock your session using

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$ light-locker-command -l

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This requires {{ic|light-locker}} to be started at the beginning of your session - see [[Autostarting]].

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== Troubleshooting ==

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If you encounter consistent screen flashing and ultimately no LightDM on boot, ensure that you have defined the greeter correctly in LightDM's config file. And if you have correctly defined the GTK greeter, make sure the {{ic|xsessions-directory}} (default: {{ic|/usr/share/xsessions}}) exists and contains at least one .desktop file.

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The same error can happen on lightdm startup if the last used session is not available anymore (eg. you last used gnome and then removed the gnome-session package): the easiest workaround is to temporarily restore the removed package. Another solution might be:

In case of your locale not being displayed correctly in Lightdm add your locale to {{ic|/etc/environment}}

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LANG=pt_PT.utf8

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Alternatively if you want LightDM and its greeters to be in a language other than your set system locale, you can use the {{ic|1=Environment=}} option in [[Systemd#Drop-in files]].

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=== Missing icons with GTK greeter ===

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If you are using {{Pkg|lightdm-gtk-greeter}} as a greeter and it shows placeholder images as icons, make sure valid icon themes and themes are installed and configured. Check the following file:

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{{hc|/etc/lightdm/lightdm-gtk-greeter.conf|2=

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[greeter]

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theme-name=mate # this should be the name of a directory under /usr/share/themes/

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icon-theme-name=mate # this should be the name of a fully featured icons set directory under /usr/share/icons/

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}}

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=== LightDM freezes on login attempt ===

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You may find that after entering the correct username and password and attempting to log in, LightDM freezes and you are unable to continue to the desktop. To fix the issue, reinstall the {{Pkg|gdk-pixbuf2}} package. See [https://bbs.archlinux.org/viewtopic.php?id=179031 this forum thread].

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=== LightDM displaying in wrong monitor ===

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If you are using multiple monitors, LightDM may display in the wrong one (e.g. if your primary monitor is on the right). To force the LightDM login screen to display on a specific monitor, edit {{ic|/etc/lightdm/lightdm.conf}} and change the ''display-setup-script'' parameter like this:

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{{hc|/etc/lightdm/lightdm.conf|2=

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display-setup-script=xrandr --output ''HDMI1'' --primary

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}}

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Replace ''HDMI1'' with your real monitor ID, which you can find from '''xrandr''' command output.

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Alternatively, if you are using the GTK+ greeter, you can edit {{ic|/etc/lightdm/lightdm-gtk-greeter.conf}} and add the ''active-monitor'' parameter like this:

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{{hc|/etc/lightdm/lightdm-gtk-greeter.conf|2=

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[greeter]

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active-monitor=0

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}}

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Replace 0 with the desired display number.

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==== Sources of Arch-centric 64x64 Icons ====

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=== LightDM does not appear ===

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The archlinux-artwork package in [extra] contains some nice examples that install to {{ic|/usr/share/archlinux/icons}} and that can be copied to {{ic|/usr/share/icons/hicolor/64x64/devices}} as follows:

It may happen that your system boots so fast that LightDM service is started before your graphics drivers are properly loaded. If this is your case, you will want to add the following config to your lightdm.conf file:

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After copying, the archlinux-artwork package can be removed.

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[LightDM]

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logind-check-graphical=true

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=== Enabling Autologin ===

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This setting will tell LightDM to wait until graphics devices are ready before spawning greeters/autostarting sessions on them.

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Edit {{ic|/etc/lightdm/lightdm.conf}} and change these lines to:

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[SeatDefaults]

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=== Pulseaudio not starting automatically ===

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autologin-user=your_user

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autologin-user-timeout=0

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pam-service=lightdm-autologin

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==== PAM settings ====

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See [[PulseAudio#Running]].

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{{Note|One Arch user found that these steps weren't needed.}}

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Lightdm goes through PAM even when autologin is enabled. You must make sure that

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=== Long pause before LightDM shows up when home is encrypted ===

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PAM allows the login without prompting for a password.

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Create a new group called, say, {{ic|autologin}} and add yourself to the group:

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Some LightDM themes try to access the user avatar located in HOME. If your HOME is encrypted, LightDM cannot access it and hangs. To prevent this from happening, you can either:

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groupadd autologin

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gpasswd -a ''username'' autologin

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Edit {{ic|/etc/pam.d/lightdm}} and locate the line "auth required pam_unix.so". Add new lines before and after it so that the section now reads:

This ensures that the user will not be asked for a password when logging in through Lightdm autologin.

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=== Missing power buttons in GTK greeter ===

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So any user you would like to login without typing password in LightDM just add to this group.

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=== NumLock ON ===

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The GTK greeter used to have a button to power off / restart the computer in the top right corner. This has been removed from the default configuration in newer versions of the upstream package ([https://bugzilla.redhat.com/show_bug.cgi?id=1506505 bug report]). To get it back, adapt the following line in {{ic|/etc/lightdm/lightdm-gtk-greeter.conf}}:

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Install the {{ic|numlockx}} package and the edit {{ic| /etc/lightdm/lightdm.conf}} adding the following line:

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greeter-setup-script=/usr/bin/numlockx on

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=== User switching under xfce4 ===

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{{hc|/etc/lightdm/lightdm-gtk-greeter.conf|2=

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With the release of xfce4 v4.10, user switching is supported natively. To use it with lightdm, users need only to create a symlink:

Installation

Installlightdm. Note that stable releases are even-numbered (1.8, 1.10) while development releases are odd-numbered (1.9, 1.11). These development releases are available with lightdm-develAUR. Also available is lightdm-bzrAUR.

Greeter

You will probably want to install a greeter. A greeter is a GUI that prompts the user for credentials, lets the user select a session, and so on. It's possible to use LightDM without a greeter, but only if an automatic login is configured. The reference greeter is lightdm-gtk-greeter. LightDM attempts to use this greeter when started unless configured to do otherwise.

You can set the default greeter by changing the [Seat:*] section of the LightDM configuration file, like so:

/etc/lightdm/lightdm.conf

[Seat:*]
...
greeter-session=lightdm-yourgreeter-greeter

Which greeters are available? What values may be assigned to the greeter-session option? Each .desktop file in the /usr/share/xgreeters directory denotes an available greeter. In this example, the lightdm-gtk-greeter and lightdm-kde-greeter greeters are available:

Enabling LightDM

Command line tool

LightDM offers a command line tool, dm-tool, which can be used to lock the current seat, switch sessions, etc, which is useful with 'minimalist' window managers and for testing. To see a list of available commands, execute:

$ dm-tool --help

User switching

The factual accuracy of this article or section is disputed.

Reason: Is this warning inappropriate? Don't dm-tool lock and dm-tool switch-to-greeter do the equivalent of calling loginctl lock-session? If your screen locker doesn't register with logind then there's nothing dm-tool ... can do - but that's not LightDM's fault. This issue is well known and touched upon here and here. (Discuss in Talk:LightDM#)

LightDM's dm-tool command can be used to allow multiple users to be logged in on separate ttys. The following will send a signal requesting that the current session be locked and then will initiate a switch to LightDM's greeter, allowing a new user to log in to the system.

Note: It is recommended to place the PNG or JPG file in /usr/share/pixmaps since the LightDM user needs read access to the wallpaper file.

GTK3 Dark Theme

GTK3 introduced "dark" alternate color palettes for themes, but lightdm-gtk-greeter does not yet support specifing one natively. A workaround is to override the theme with an evironment variable in /usr/share/xgreeters/lightdm-gtk-greeter.desktop For example:

/usr/share/xgreeters/lightdm-gtk-greeter.desktop

[Desktop Entry]
Name=LightDM GTK+ Greeter
Comment=This runs the GTK+ greeter, it should only be run from LightDM
Exec=env GTK_THEME=Adwaita:dark lightdm-gtk-greeter
Type=Application
X-Ubuntu-Gettext-Domain=lightdm

Webkit2 greeter

The lightdm-webkit2-greeterAUR allows you to choose a background image directly on the login screen. It also offers an option to display a random image each time it starts. By default, images are sourced from /usr/share/backgrounds. You can change the background images directory by editing lightdm-webkit2-greeter.conf. For example:

/etc/lightdm/lightdm-webkit2-greeter.conf

[branding]
background_images = /usr/share/backgrounds

Note: The background images directory must be accessible to the LightDM user so it should not be located anywhere under /home.

Unity greeter

Users using the lightdm-unity-greeterAUR must edit the /usr/share/glib-2.0/schemas/com.canonical.unity-greeter.gschema.xml file and then execute:

Changing your avatar

Tip: If you are using KDE, you can change your avatar in KDE System Settings.

First, make sure the accountsservice package from the official repositories is installed, then set it up as follows, replacing username with the desired user's login name. The .png file extension should not be included in the filename.

Edit or create the file /var/lib/AccountsService/users/username, and add the lines

[User]
Icon=/var/lib/AccountsService/icons/username

Create the file /var/lib/AccountsService/icons/username using a 96x96 PNG image file.

Note: Make sure that both created files have 644 permissions, use chmod to correct them.

Sources of Arch-centric 64x64 icons

The archlinux-artworkAUR package from the AUR contains some nice examples that install to /usr/share/archlinux/icons and that can be copied to /usr/share/icons/hicolor/64x64/devices as follows:

Enabling interactive passwordless login

You must then also be part of the nopasswdlogin group to be able to login interactively without entering your password:

# groupadd -r nopasswdlogin
# gpasswd -a username nopasswdlogin

Note: GNOME users, and by extension any gnome-keyring user may have to follow the instructions at the end of the previous section on enabling autologin.

To create a new user account that logs in automatically and additionally able to login again without a password the user can be created with supplementary membership of both groups, e.g.:

# useradd -mG autologin,nopasswdlogin -s /bin/bash username

Hiding system and services users

To prevent system users from showing-up in the login, install the optional dependency accountsservice, or add the user names to /etc/lightdm/users.conf under hidden-users. The first option has the advantage of not needing to update the list when more users are added or removed.

Default session

Adjusting the login window's position

GTK+ greeter

Users need to edit /etc/lightdm/lightdm-gtk-greeter.conf and enter a value for the position variable. It accepts x and y values, either absolute (in pixels) or relative (in percent). Each value can also have an additional anchor location for the window, start, center and end separated from the value by a comma.

Example:

position=200,start 50%,center

VNC Server

Lightdm can also be used to connect to via VNC. Make sure to install tigervnc on the server side and optionally as your VNC client on the client PC.

Setup an authentication password on the server as root:

# vncpasswd /etc/vncpasswd

Edit the LightDM configuration file as shown below. Note that listen-address configures the VNC to only listen to connections from localhost. This is used to only allow connections via SSH and port forwarding. On the SSH client, make sure that you use localhost:5900 for the tunnel destination; using 127.0.0.1:5900 or ::1:5900 is not reliable on dual stack network connections. If you want to allow insecure connections you can disable this setting.

Note: If you get a blank screen upon opening the VNC connection, try a different LightDM greeter.

Lock the screen using light-locker

light-locker is a simple screen locker using LightDM to authenticate the user. Once it is installed and running you can lock your session using

$ light-locker-command -l

This requires light-locker to be started at the beginning of your session - see Autostarting.

Troubleshooting

If you encounter consistent screen flashing and ultimately no LightDM on boot, ensure that you have defined the greeter correctly in LightDM's config file. And if you have correctly defined the GTK greeter, make sure the xsessions-directory (default: /usr/share/xsessions) exists and contains at least one .desktop file.

The same error can happen on lightdm startup if the last used session is not available anymore (eg. you last used gnome and then removed the gnome-session package): the easiest workaround is to temporarily restore the removed package. Another solution might be:

Wrong locale displayed

In case of your locale not being displayed correctly in Lightdm add your locale to /etc/environment

LANG=pt_PT.utf8

Alternatively if you want LightDM and its greeters to be in a language other than your set system locale, you can use the Environment= option in Systemd#Drop-in files.

Missing icons with GTK greeter

If you are using lightdm-gtk-greeter as a greeter and it shows placeholder images as icons, make sure valid icon themes and themes are installed and configured. Check the following file:

/etc/lightdm/lightdm-gtk-greeter.conf

[greeter]
theme-name=mate # this should be the name of a directory under /usr/share/themes/
icon-theme-name=mate # this should be the name of a fully featured icons set directory under /usr/share/icons/

LightDM freezes on login attempt

You may find that after entering the correct username and password and attempting to log in, LightDM freezes and you are unable to continue to the desktop. To fix the issue, reinstall the gdk-pixbuf2 package. See this forum thread.

LightDM displaying in wrong monitor

If you are using multiple monitors, LightDM may display in the wrong one (e.g. if your primary monitor is on the right). To force the LightDM login screen to display on a specific monitor, edit /etc/lightdm/lightdm.conf and change the display-setup-script parameter like this:

/etc/lightdm/lightdm.conf

display-setup-script=xrandr --output HDMI1 --primary

Replace HDMI1 with your real monitor ID, which you can find from xrandr command output.

Alternatively, if you are using the GTK+ greeter, you can edit /etc/lightdm/lightdm-gtk-greeter.conf and add the active-monitor parameter like this:

/etc/lightdm/lightdm-gtk-greeter.conf

[greeter]
active-monitor=0

Replace 0 with the desired display number.

LightDM does not appear

It may happen that your system boots so fast that LightDM service is started before your graphics drivers are properly loaded. If this is your case, you will want to add the following config to your lightdm.conf file:

[LightDM]
logind-check-graphical=true

This setting will tell LightDM to wait until graphics devices are ready before spawning greeters/autostarting sessions on them.

Missing power buttons in GTK greeter

The GTK greeter used to have a button to power off / restart the computer in the top right corner. This has been removed from the default configuration in newer versions of the upstream package (bug report). To get it back, adapt the following line in /etc/lightdm/lightdm-gtk-greeter.conf: